LIBTD-1314: Parse SEAMUS db dump into usable format

Created simple rake task and Wordpress class for parsing a Wordpress xml dump from SEAMUS and extracting authors and work items.

$ bin/rake seamus:extract_items["input.xml"]
$ bin/rake seamus:extract_authors["input.xml"]

This will eventually be used later as a starting point for importing data into COMPEL.

Note: Example wordpress dump can be found here: https://webapps.es.vt.edu/jira/browse/LIBTD-1313